Catalytic production of hydrogen and carbon nanotubes from glycerol via Ni2⁺/Zr⁴⁺-doped double-hydroxide layers

Well-dispersed NiZrAl catalysts were prepared by thermally decomposing the NiZrAl-layered double hydroxides (LDH) precursor which was in situ assembled on Al2O3 (Al source) surface through a urea homogeneous precipitation-deposition strategy, characterized by XRD, TG, TEM, N2 adsorption/desorption isotherms, TPR, XPS, H2-chemisorption and Raman techniques. The findings indicated that nickel species were well-dispersed on the support surface. Variation in nickel loading had a more significant influence on the surface chemical state and dispersion. Nickel oxide was only partially reduced to metallic Ni, and larger number and smaller metal particle size of which were more favorable for glycerol cracking. The product distribution was markedly affected by the content of oxygen vacancies, and hydrogen production was enhanced by promoting the water gas shift reaction. The optimal catalytic performance was achieved over the sample 15NiZr@Al2O3 with a glycerol conversion of 92.4 % and a H2 selectivity of 76.7 %. All the catalysts demonstrated good resistance to sintering, and carbon nanotubes were generated as a by-product.